/Engine/Source/Runtime/GeometryCore/Public/DynamicMesh/InfoTypes.h
Note that cycling or permuting the vertices of a triangle will change these indices.
struct FMeshTriEdgeID
unsigned:  30
TriangleID
The index of the mesh Triangle
unsigned:  2
TriEdgeIndex
The 0/1/2 index of the edge in the triangle's tuple of edges